The present invention relates to a semiconductor device and a method of forming the same, and more particularly to a copper-alloy interconnection structure formed in an inter-layer insulator in a semiconductor device and a method of forming the same.
In recent years, the degree of integration of semiconductor devices such as LSI has been on the increase in response to the requirements for improvement in functions of electronic devices and for scaling down and reduction in weight as well as improvement in high speed performance. In order to realize the increase in the degree of integration of the semiconductor devices, it is essential to reduce a width of the interconnection. The majority of the conventional interconnection comprises an aluminum interconnection because aluminum is low in electrical resistance and is superior in adhesiveness with a silicon dioxide film as well as superior in formability.
The aluminum interconnection raises serious problems in electromigration, stressmigration, and formation of voids particularly as the width of the aluminum interconnection is reduced for realizing the increase in the degree of integration of the semiconductor devices. In these circumstances, recently, other available materials than aluminum have been investigated as the interconnection materials free from the above problems.
Copper is attractive as the interconnection material reduced in width. Copper is lower in electric resistance than aluminum. Namely, the electric resistance of copper is about two third of the electric resistance of aluminum. For this reason, the copper interconnection allows a higher current density than the aluminum interconnection. Further, copper is higher in melting point than aluminum by not less than 400xc2x0 C. This means that the copper interconnection is higher in stability to electromigration than the aluminum interconnection. The copper interconnection is, thus, attractive as the interconnection material for the advanced semiconductor device such as LSI.
If, however, the width of the copper interconnection is reduced to about 0.3 micrometers, then an electromigration is caused, and the copper interconnection is made deteriorated due to an electromigration. In order to reduce the electromigration of the copper interconnection having a reduced with of about 0.3 micrometers, it is effective to enlarge crystal grain sizes of copper of the copper interconnection. The enlargement in crystal grain size of copper causes grain boundaries of the crystal grain to be diffused, thereby suppressing movement of copper atoms through the copper interconnection. The suppression of the movement of copper atoms through the copper interconnection means suppression of electromigration. In Japanese laid-open patent publication No. 4-326521, it is disclosed that a copper interconnection has a copper crystal grain size of not less than 1 micrometer. This copper interconnection may be formed by a deposition of a copper film on an insulation film on a semiconductor substrate by either a molecular beam epitaxy or a sputtering method, and subsequent patterning the copper film by a dry etching process. Similar conventional techniques are also disclosed in Japanese laid-open patent publication No. 5-47760 and 10-60633.
In order to realize the reduction in width of the interconnection, it is required to accurately and conveniently form the interconnection. For this purpose, in place of the above method of deposition of the copper film and subsequent patterning the same by a dry etching process, the following method has been proposed. A groove is formed in an insulation film on a semiconductor substrate. A copper film is filled within the groove for subsequent heat treatment to form a copper interconnection in the groove. This conventional method is suitable for forming a fine copper interconnection with a reduced width. It is not so difficult to accurately control the width of the groove in the insulation film. This means it not so difficult to accurately control the width of the copper interconnection in the groove. FIG. 1A is a fragmentary cross sectional elevation view illustrative of a conventional copper interconnection formed in a trench groove in an insulation film over a semiconductor substrate, taken along a plane vertical to a longitudinal direction of the copper interconnection. FIG. 1B is a fragmentary perspective view illustrative of the conventional copper interconnection of FIG. 1A. FIG. 1C is a fragmentary cross sectional elevation view illustrative of the conventional copper interconnection, taken along a B-Bxe2x80x2 line of FIG 1B, wherein the B-Bxe2x80x2 line is parallel to the longitudinal direction of the copper interconnection. FIGS. 2A through 2D are fragmentary cross sectional elevation views illustrative of sequential steps involved in a conventional method of forming a copper interconnection formed in a trench groove in an insulation film over a semiconductor substrate, taken along a plane vertical to a longitudinal direction of the copper interconnection.
A copper interconnection 400 comprises a copper layer 41 and a barrier material layer 2. The copper interconnection 400 is formed in a trench groove formed in an inter-layer insulator 10 formed on a semiconductor substrate 0. The barrier metal layer 2 is formed on a bottom and side walls of the trench groove and the copper layer 41 is formed on the barrier metal layer 2 to fill the trench groove. A top surface 400a of the copper film 41 of the copper interconnection 400 is planarized to be leveled to the top surface of the inter-layer insulator 10. The copper interconnection 400 may be formed as follows.
With reference to FIG. 2A, a trench groove 10a is formed in an inter-layer insulator 10 on a semiconductor substrate 0.
With reference to FIG. 2B, a barrier metal layer 2 is entirely formed on the top surface of the inter-layer insulator 10 and on a bottom and side wails of the trench groove 10a. 
With reference to FIG. 2C, a copper layer 12 is entirely deposited on the barrier metal layer 2 so that the trench groove 10a is completely filled with the copper layer 12 and also the copper layer 12 exists over the top surface of the inter-layer insulator 10.
With reference to FIG. 2D, a chemical mechanical polishment is carried out to the copper layer 12 and the barrier metal layer 2 so that the copper layer 12 and the barrier metal layer 2 remain only with in the trench groove 10a to form a copper layer 41 within the trench groove 10a. A heat treatment is carried out to the copper layer 41 so as to cause re-arrangement of copper atoms of the copper layer 41, thereby to form a copper interconnection 400 in the trench groove in the inter-layer insulator 10.
As a modification, it is possible that the heat treatment is carried out prior to the chemical mechanical polishment.
This conventional copper interconnection has the following problems. As described above, the trench groove 10a is formed in the inter-layer insulator and then the copper layer is filled within the trench groove prior to the heat treatment to the copper layer for re-arrangement of the copper atoms in the copper layer. If the copper interconnection is required to have a reduced width, it is necessary to form the trench groove with a reduced width corresponding to the required reduced width of the copper interconnection. The narrow width of the trench groove suppress the growth of the copper crystal grain, whereby the copper crystal grain is likely to have a small size. The small size of the crystal grain allows existence of many crystal grain boundaries 43. During the current flow through the copper interconnection, a mass-transfer of copper frequently appears through crystal grain boundaries having the lowest energy, whereby the electromigration frequently appears. This electromigration may cause a disconnection or a crack of the copper interconnection. As a result, the electromigration reduces the reliability of the copper interconnection and the yield of the semiconductor device having the copper interconnection as well as reduces the productivity.
In the above circumstances, it had been required to develop a novel copper interconnection free from the above problem.
Accordingly, it is an object of the present invention to provide a novel copper-alloy interconnection free from the above problems.
It is a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has crystal grains with large sizes and reduced grain boundary.
It is a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a reduced mass-transfer path for copper atoms.
It is a still further object of the present invention to provide a novel copper-alloy interconnection in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is capable of suppressing electromigration.
It is yet a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a disconnection of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a crack of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a high reliability.
It is yet a further object of the present invention to provide a novel copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a high productivity.
It is another object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection free from the above problems.
It is a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has crystal grains with large sizes and reduced grain boundary.
It is a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a reduced mass-transfer path for copper atoms.
It is a still further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is capable of suppressing electromigration.
It is yet a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a disconnection of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a crack of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a high reliability.
It is yet a further object of the present invention to provide a novel semiconductor device having an improved copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a high productivity.
It is another object of the present invention to provide a novel method of forming a copper-alloy interconnection free from the above problems.
It is a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has crystal grains with large sizes and reduced grain boundary.
It is a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a reduced mass-transfer path for copper atoms.
It is a still further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is capable of suppressing electromigration.
It is yet a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a disconnection of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection is free from a crack of the copper-alloy interconnection.
It is yet a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation film, wherein the copper-alloy interconnection has a high reliability.
It is yet a further object of the present invention to provide a novel method of forming a copper-alloy interconnection formed in a narrow trench groove of an insulation films wherein the copper-alloy interconnection has a high productivity.
The present invention provides an electrically conductive layer comprising a copper alloy which includes at least one of Ag, As, Bi, P, Sb, Si, and Ti in the range of not less than 0.1 percent by weight to not more than a maximum solubility limit to copper, so that the copper alloy is in a solid solution and/or which includes at least one of Mo, Ta and W in a range of not less than 0.1 percent by weight to not more than 1 percent by weight.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.